1. Field of the Invention
The present invention relates to high-frequency electronic parts and particularly to a dielectric resonator to be used in microwave and millimeter wave bands and a dielectric filter, dielectric duplexer, oscillator, and communication device using such.
2. Description of the Related Art
A first example of a conventional dielectric filter is explained with reference to FIG. 26.
The dielectric filter 110a comprises a dielectric substrate 120a on the opposing upper and lower surfaces of which electrodes are arranged, a lower case 112, and an upper case 111. By removing part of the upper electrode five round electrodeless portions 121a through 121e are formed. In like manner, electrodeless portions 121axe2x80x2 through 121exe2x80x2 (not shown) of the same shape are formed at the corresponding locations of the lower electrode. A dielectric resonator 122a is composed of a dielectric substance between the electrodeless portions 121a and 121axe2x80x2 and the upper and lower cases 111 and 112 surrounding the substance. Other pairs of the electrodeless portions also constitute dielectric resonators likewise. The resonance frequency of each of the resonators depends on the shape of the electrodeless portions 121a through 121e, the thickness of the dielectric substrate 120a, etc.
The lower case 112 is made up of a substrate 113 and a metal frame 114 placed on the substrate. Inside the metal frame 114 a support 115 to support the dielectric substrate 120a is formed. On substantially the whole upper surface of the substrate 113 an electrode 116 is arranged. Part of the electrode 116 is removed, and in the electrodeless portion microstrip lines 130 and 131 are arranged. These lines function as input-output lines of the filter 110a. Further, on nearly the whole surface of the bottom of the substrate 113 an electrode 116xe2x80x2 (not shown) is arranged.
In this filter, for example, the TE010 resonance mode of each of the dielectric resonators is used. When a signal is input into the microstrip line 130, the microstrip line 130 and the dielectric resonator 122a are electromagnetically coupled. Further, through the coupling between the neighboring dielectric resonators 122a through 122e a signal is output from the microstrip line 131 on the output side. As a result, the dielectric filter 110a functions as a five-stage bandpass filter. The non-loaded Q of a dielectric resonator using the TE010 mode is higher than the non-loaded Q of a dielectric resonator having a rectangular slot, which will be described later. For example, at 26 GHz the non-loaded Q of the former is about 1900 and the non-loaded Q of the latter is about 900. Thus, when TE010 mode is used, non-loaded Q of the dielectric resonators is high, and accordingly there is an advantage of being able to obtain a dielectric filter with a small insertion loss.
Next, a second example of a conventional dielectric filters is explained with reference to FIG. 27.
In a dielectric filter 110b, the shape of the electrodeless portions 1121f through 1121j of the electrode is rectangular. The shape of the electrodeless portions on the lower surface of the substrate 1120b is the same. By making the shape of the electrodeless portions 1121f through 1121j rectangular, a rectangular slot mode is used as a resonance mode. For example, the TE102 mode, which is a rectangular slot mode, can be used. When a rectangular slot mode is used, the amount of an electromagnetic field leaking outside the resonator increases, compared with the case where the TE010 mode is used, and the degree of coupling between the input-output lines and the resonators and between the dielectric resonators 1122f through 1122j increases.
In the dielectric filter to be used in a communication device, a sufficient damping characteristic is required in the vicinity of a pass band. Generally, dielectric resonators constituting a dielectric filter have many resonance modes, and there are cases where the resonance frequencies of undesired resonance modes exist in the vicinity of the resonance frequencies of resonance modes to be used. In such cases, by changing the diameter of the resonators and the thickness of the dielectric substrate adjustment takes place so that the resonance frequencies of both modes are separated from each other. However, in the above conventional filters the separation of the resonance frequencies of both modes could not be effectively separated.
FIG. 28 shows the relationship between the resonance frequency and the resonator""s diameter of the dielectric resonators contained in the dielectric filter 110a. The solid line represents the TE010 mode as a resonance mode to be used, and the broken line the HE310 mode which is an undesired resonance mode. Further, FIG. 29 shows the relationship of the resonance frequency to the resonator length (here, resonator length measured along the direction in which the plurality of resonators are arranged) in the dielectric filter 110b. The solid line represents the TE102 mode as a resonance mode to be used, the broken line the TM111 mode as an undesired resonance mode, and the one-dot chain line the TM112 mode as another undesired resonance mode.
As understood in FIGS. 28 and 29, even if the sizes or shapes, etc., are changed in these dielectric resonators, the resonance frequency of an undesired resonance mode can not be so effectively separated from the resonance frequency of a resonance mode to be used.
According to the present invention, a dielectric resonator, dielectric filter, dielectric duplexer, oscillator, and communication device which have a good transmission characteristic or reflection characteristic are provided by separating the resonance frequency of an undesired resonance mode sufficiently far from the resonance frequency of a resonance mode to be used.
A dielectric resonator according to one aspect of the present invention comprises a dielectric substrate having two opposing two main surfaces, on which surface electrodes are formed. Electrodeless portions are formed in the surface electrodes, and a conductor is arranged a fixed distance away from the dielectric substrate. At least one electrode projection portion which projects into the electrodeless portion is provided in the boundary portion between the electrodeless portion and the electrode.
Further, a dielectric resonator according to a second aspect of the present invention comprises a dielectric substrate on the two opposing main surfaces on which surface electrodes are formed, electrodeless portions formed in the surface electrodes on the two main surfaces, and a conductor arranged a fixed distance away from the dielectric substrate, wherein at least one electrode recessed portion is formed in the surface electrode in the boundary portion between the electrodeless portion and the electrode.
Further, at least one projection portion and at least one recessed portion may be combined in a single dielectric resonator.
These projection and recessed portions can have an influence on the resonance frequencies of various resonance modes existing in a dielectric resonator and can separate the resonance frequencies of undesired resonance modes away from the resonance frequencies of resonance modes to be used.
Further, in a dielectric resonator of the present invention, the electrode projection portions can be arranged at fixed locations corresponding to undesired resonance modes in the dielectric resonator, respectively.
Further, in a dielectric resonator of the present invention, the recessed portions of electrode can be arranged at fixed locations corresponding to undesired resonance modes in the dielectric resonator, respectively.
These projection and recessed portions can change the resonance frequency of an undesired resonance mode most affecting the resonance mode to be used, that is, the undesired resonance mode having a resonance frequency closest to the resonance frequency of the resonance mode to be used. Further, by changing the location, shape, size, etc., of the electrode projection portion or recessed portion, the resonance frequency of an undesired resonance mode can be easily set.
Further, a dielectric filter of the present invention comprises the above dielectric resonator and an input-output connectors.
Further, a dielectric duplexer of the present invention comprises at least two dielectric filters, input-output connectors to be connected respectively to the dielectric filters, and an antenna connection means to be commonly connected to both dielectric filters, wherein at least one of the dielectric filters is composed of the above dielectric filter.
Further, a communication device of the present invention comprises the above dielectric duplexer, a transmission circuit to be connected to one of the input-output connectors of the dielectric duplexer, a reception circuit to be connected to the other input-output connector, and an antenna to be connected to the antenna connector of the dielectric duplexer.
Further, an oscillator of the present invention comprises the above dielectric resonator, an enclosure to contain the dielectric resonator, and a circuit board.
Further, another communication device of the present invention comprises at least a transmission circuit or a reception circuit, and/or an antenna, wherein the transmission circuit or reception circuit contains the above oscillator.
Because of the above features, a dielectric filter, dielectric duplexer, oscillator, and communication device having a good transmission characteristic or reflection characteristic can be obtained.
Other features and advantages of the invention will be understood from the following detailed description of embodiments thereof, wherein like references denote like elements and parts.